Many electronic circuits have a need for thermal protection. Without thermal protection, the electronic circuit or nearby components can be damaged, or at least rendered less efficient. Voltage regulators and battery chargers are two examples of circuits needing thermal protection, although many other circuits also need thermal protection. In the case of a battery charging circuit, overheating can damage the battery and even lead to risk of the battery exploding. Without a thermal protection circuit, overheating can easily happen due to the charging current passing through elements having some resistance. For example, battery chargers often have power pass devices that generate significant heat when passing the charging current. In some cases, the power pass devices are constructed external to the integrated circuit containing the rest of the circuit to reduce the heating problem. However, this complicates the circuit design and increases manufacturing expense. Moreover, other circuit elements on the integrated circuit also dissipate heat.
One technique for thermal protection is to measure the temperature on the integrated circuit die or at another significant location and shut down the circuit if the temperature gets too high. Once the temperature has returned to below a safe limit, the power to the circuit is abruptly switched back on. Unfortunately, turning the circuit off and on causes “bounce”, which stresses the integrated circuit.
Thus, a need exists for a thermal protection circuit for an electronic circuit. A still further need exists for a thermal protection circuit that does not cause unnecessary stress to the power delivery system it protects. A still further need exists for a thermal protection circuit that is compatible with and can be fabricated economically with existing semiconductor fabrication techniques.